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The cat as a carnivore: proteins, carbohydrates and beyond…

Lee Danks, in the 10th of his series for Royal Canin, reminds us of cats' carnivorous nature.

that the cats we care for are obligate
carnivores. What might be useful to
review is not only what this truly means,
but what consequences this has for the
individual in their everyday health.

Where we and pet owners take many decisions in feeding, we should
all be aware of
and respect the
nutritional needs
of those in our care. Obligate carnivore
physiology makes for unique food-
animal interactions which influence not only daily requirements, but the
predispositions and reactions cats have
in certain conditions.

Considering how the cat’s nutritional
idiosyncrasies influence their needs in
a state of both wellness and ill health
awakens us to the reality that these pets
are certainly not, after all, small dogs.

As obligate carnivores, cats rely on
nutrients in animal tissues to meet their
specific requirements. According to
FEDIAF (The European Pet Food
Industry Federation, setting a regulatory
framework for the production of safe
and nutritious pet food), omnivorous
dogs require 45g of protein for every
1,000 kilocalories they consume.

In contrast, feline patients require
a minimum of 62.5g per 1,000
kilocalories.5 This is the starting point
by which we apply the above definition,
founded on years of collective research
and understanding of cats’ needs.

Protein and amino acid requirements

Just as in any other species, historical
feeding habits have led to many
biochemical adaptations. In the cat, this
is associated with the consumption of
prey species.

With an ancestrally high-meat diet,
cats are metabolically adapted to
preferentially use protein as an energy
source for maintenance of blood
glucose concentrations. As a result,
they have a higher basal need for
nitrogen and an increased requirement
of essential amino acids.

Several contributors to this phenomenon have been investigated;
most notably cats have been shown to
not adapt to the activity of protein-
catabolising aminotransferases or urea-
cycle enzymes.

Even in the case of low dietary
supply, the obligate carnivore
is suggested to
continually utilise
protein not just
for structural and
synthetic purposes,
but for providing
energy. This is one of the central reasons for adhering to
the daily allowance recommendations
above and is also an important
consideration for avoiding protein
malnutrition which can occur more
quickly in the sick, injured or anorexic

Eleven amino acids are recognised
as essential to the feline species and
quite a number are needed in increased
amounts as their utilisation is higher:

  • Taurine (for vision, cardiac muscle
    function and the function of nervous,
    reproductive and immune systems)
    – endogenous synthetic enzymes are
    minimally active and cats have an
    obligatory loss of taurine into the bile.
  • Arginine (used in the urea cycle
    which is not regulated even when food
    is withheld) – synthetic pathways are
    poorly developed in the cat and this
    amino acid should be considered in
    cats with hepatic lipidosis.
  • Methionine and cysteine
    (incorporated into antioxidants, hair
    and urinary outputs, but primarily as
    gluconeogenic amino acids, catabolised
    to provide energy).
    Tyrosine and carnitine –
    conditionally essential amino acids.

Carbohydrate considerations

Respecting that there’s likely a giant
leap from ancestral feeding habits to
those of modern wild populations,
we may still reflect on the typical
macronutrient content of the prey
that feral cats consume. Estimates on
the “composition” of small mammals,
birds, reptiles, amphibians and insects
tell us that less than 10% of calories
consumed by a feral cat come from

Just the same as protein-digestion
and utilisation is unique to the obligate
carnivore, so is their response to
carbohydrate. Cats don’t have an
essential need for dietary carbohydrate.
When compared to dogs for example,
they have lower activities of intestinal
and pancreatic amylases and intestinal
disaccharidases, which break down
carbohydrate in the small intestines.10,11
They have low glucokinase and
glycogen synthetase levels in the liver
and, given their historically consistent
supply, protein and fat are often used
as gluconeogenic fuels, releasing
glucose in “continuous boluses over a
long time frame”.

This does not mean that cats cannot
use digestible carbohydrate at all as
an energy source. Albeit at a reduced
capacity than the typical omnivore or
herbivore, they are quite efficient in
their use of simple sugars, particularly
when energy yields are important. One
key physiological indication for this is during gestation, particularly where
lipoproteins cannot cross the placental

Complex carbohydrates which are
more resistant to digestion can play a
role in moderating intestinal function,
but species-specific tolerances
should always be taken into account.
Commonly referred to as fibre, these
can affect intestinal passage, faecal
pH, microbiome and intestinal water

Carnivore-linked disorders?

In one hallmark publication, The
Carnivore Connection
3, the cat’s ancestral
consumption patterns have been
compared to ice-age human eating
habits. At this time, man generally
consumed hunted meat with some
supplementation from gathered fruits
and vegetable matter, contributing
relatively small amounts of sugars and fibre.

In this nutritional context, a
heightened hepatic gluconeogenic
capacity and a “baseline” insulin
resistance (reduced peripheral glucose utilisation) is described. This adaptation
is said to give survival advantage,
particularly in the case of reproduction,
where foetal growth and lactation draw
heavily on dietary glucose supplies.

With time, many human populations
embraced the high nutritional yields
that developing agriculture had to offer,
moving to higher plant-based, higher-
carb diets as a consequence.

Select tribes didn’t change in
this manner and continued to eat
a meat-based diet and it is among
these populations (the Paleo-Indians,
Australian Aborigines and Paci c
Islanders for example) a higher
incidence of carbohydrate-sensitive
conditions (namely diabetes and
obesity) is found.3 This “carnivore
connection”, whereby glucose
intolerance, insulin resistance and
diabetic consequences occur on
exposure to high carbohydrate rations,
has been extrapolated from human to

For all of this theory, the inference
that cats exist in an insulin-resistant
state is not supported by the
references cited in the above article. On investigation, experimentally
induced hyperglycaemia is found to
be detrimental to pancreatic b-cells in
cats, but at the glucose levels quoted,
an equal effect was seen in omnivorous

The level of starch delivered via
extruded dry diets is not significant
enough to produce extraordinary
hyperglycaemia in cats compared to
other species. Additionally, one
study1 measured long-term effects on
glucose tolerance, insulin sensitivity
and insulin secretion within two
standardised groups of colony cats
(n=13 young cats [median 1.1 years] vs
n=12 older cats [median 5.8 years]), fed
a dry diet of 35% metablolisable energy
as carbohydrate, from weaning.

The diet was estimated as six times
greater in carbohydrate content than
that provided in a diet of prey. The
mature cats consumed the dry diet an
average four years longer than those in the younger group: when fed long-
term, insulin sensitivity was found not
to be diminished with age.

Interestingly, differences in
insulin sensitivity and secretion were
only observed when body weights
were dissimilar, suggesting that an
overweight/obese status is more likely
to induce pre-diabetic conditions than
is dietary carbohydrate.

We have an obligation to our cats to
provide a diet which fuels the needs
of an obligate carnivore. This means
respecting the guidelines set out by the
authorities in dog and cat nutrition,
namely the National Research
Council, whose reference figures are
put into a practicable framework by
FEDIAF, and then equally upheld as
“best practice” by the UK’s Pet Food
Manufacturers’ Association (PFMA).

What we might describe as “higher
quality” cat foods will not only ful l
legal recommended minimums for
protein, but consider the source,
processing, digestibility, aromatic
pro le and amino acid balance of each
protein in the diet.

As for carbohydrate, there is
no denying the need to include
this macronutrient group within
commercial dry pet food formulas. The
carbohydrate fraction within extruded
diets combines with other nutrients
and is suspended in a “gelatinised dough”. This composition is essential
to the cooking process, allowing kibble
expansion into a stable, palatable
format when cut and dried.

Convenience of feeding and
storage, preservation, pet preferences,
maintenance of oral hygiene and cost
are often mentioned in reference to
dry-diet benefits but at all levels, a
consciousness of protein and amino
acid profile should prevail whenever
feeding an obligate carnivore.

We all identify cats as unique in
most characteristics, and realise the
nutritional category in which they lie.
The obligate carnivore’s nutritional
biochemistry is distinctive, and we
should all be able to make a species-
specific dietary recommendation both
for everyday health and as a reaction to
the conditions we often diagnose.

References and further reading

1. Backus, R., Cave, N., Ganjam, V., Turner, J.
and Biourge, V. (2010) Age and body weight
effects on glucose and insulin tolerance in colony
cats maintained since weaning on high dietary
carbohydrate. Journal of Animal Physiology and
Animal Nutrition
94 (6): e318-328.

2. Backus, R. (2009) Controversy over carbohydrate in
diets for cats
. 2009 American College of Veterinary
Internal Medicine Forum/Canadian Veterinary
Medical Association Convention, Montreal QC,

3. Brand Miller, J. and Colagiuri, S. (1994) The
carnivore connection: dietary carbohydrate in
the evolution of NIDDM. Diabetologia 37 (12): 1,280-1,286.

4. Colagiuri, S. and Brand Miller, J.
(2002) The ‘carnivore connection’
– evolutionary aspects of insulin
resistance. European Journal of
Clinical Nutrition
56: S30-35.

5. F.E.D.I.A.F. (2012) Nutritional
guidelines for complete and
complementary pet food for dogs
and cats
. European Pet Food
Industry Federation. Available
pdf; accessed 15/10/16.

6. Hewson-Hughes, K., Gilham,
M., Upton, S., Colyer, A.,
Butterwick, R. and Miller, A. (2011) The effect of
dietary starch level on postprandial glucose and
insulin concentrations in cats and dogs. British
Journal of Nutrition
106 (S1): S105-S109.

7. Imamura, T., Kof er, M., Helderman, J.,
Prince, D., Thirlby, R., Inman, L. and Unger,
R. (1988) Severe diabetes induced in subtotally
depancreatized dogs by sustained hyperglycemia.
Diabetes 37: 600-609.

8. Kienzle, E. (2004) Blood sugar levels and
renal sugar excretion after the intake of high
carbohydrate diets in cats. Journal of Nutrition 124:

9. Kienzle, E. (1994) Effect of Carbohydrates on
Digestion in the Cat. Journal of Nutrition 124 (12):
10. Kienzle, E. (1996) Carbohydrate metabolism
in the cat.

10. Activity of amylase in the
gastrointestinal tract of the cat. Journal of Animal
Physiology and Animal Nutrition
69 (1-5): 92-101.

11. Kienzle, E. (1996) Carbohydrate metabolism
of the cat

12. Digestion of starch. Journal of Animal
Physiology and Animal Nutrition
69 (1-5): 102-114.
12. Kirk, C., Debraekeleer, J. and Armstrong, P. (2000) Normal Cats. In: Hand, M., Thatcher,
C., Remillard, R. et al (eds). Small Animal Clinical
(4th ed). Philadelphia, WB Saunders;

13. de-Oliveira, L., Carcio , A., Oliveira, M.,
Vasconcellos, R., Bazolli, R., Pereira, G. and
Prada, F. (2008) Effects of six carbohydrate
sources on diet digestibility and postprandial
glucose and insulin responses in cats. Journal of
Animal Science
86: 2,237-2,246.

14. Rogers, Q. and Morris, J. (1979) Essentiality
of amino acids for the growing kitten. Journal of
109 (4): 718-723.

15. Zoran, D. (2002) The carnivore connection to
nutrition in cats. Journal of the American Veterinary
Medical Association
221 (11): 1,559-1,567.

16. Zini, E., Osto, M., Franchini, M., Guscetti,
F., Donath, M., Perren, A., Heller, R., Linscheid,
P., Bouwman, M., Ackermann, M., Lutz, T.
and Reusch, C. (2009) Hyperglycaemia but not
hyperlipidaemia causes beta cell dysfunction and
beta cell loss in the domestic cat. Diabetologia 52:

With thanks to Rosie Mann for proofreading
this article.

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